Bacterial Siderophores That Evade or Overwhelm Lipocalin 2 Induce Hypoxia Inducible Factor 1α and Proinflammatory Cytokine Secretion in Cultured Respiratory Epithelial Cells
Bacterial Siderophores That Evade or Overwhelm Lipocalin 2 Induce Hypoxia Inducible Factor 1α and Proinflammatory Cytokine Secretion in Cultured Respiratory Epithelial Cells
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DOI：
10.1128/iai.01849-14
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发表时间：
2014-09-01
影响因子：
3.1
通讯作者：
Bachman, Michael A.
中科院分区：
文献类型：
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作者：
Holden, Victoria I.;Lenio, Steven;Bachman, Michael A.
铁是许多细胞过程所必需的，也是细菌复制所必需的。为了从宿主获取铁，致病性革兰氏阴性菌分泌铁载体，包括肠杆菌素(Ent)。然而，Ent与宿主蛋白Lipocalin 2(Lcn2)结合，阻止细菌重新摄取Fe3或Fe3+Ent。此外，与单独刺激相比，Ent和Lcn2(Ent+Lcn2)联合使用可促进IL-8的分泌。修饰的或结构不同的铁载体，包括yersiniabactin(Ybt)和糖基化Ent(GlyEnt，或salmochelin)，尽管存在Lcn2，但仍能向细菌输送铁。我们假设，对Ent和Lcn2的强大免疫反应需要铁络合作用，而不是Ent+Lcn2复合体本身，也可以被Lcn2逃逸的铁载体刺激。为了验证这一假设，用纯化的铁载体和Lcn2的组合刺激培养的呼吸道上皮细胞，并用基因表达微阵列、定量PCR和细胞因子免疫分析进行分析。Et使HIF-1α蛋白稳定，诱导受低氧诱导因子1α(HIF-1α)调控的基因表达，抑制细胞周期和DNA复制相关基因的表达，而Lcn2诱导促炎细胞因子的表达。过量的Ent或Ybt的铁络合显著增加了Lcn2诱导的IL-8、IL-6和CCL20的分泌。HIF-1α的稳定足以增强Lcn2诱导的IL-6分泌。这些数据表明，呼吸道上皮细胞可以通过增加促炎细胞因子的产生来响应细菌铁载体，从而逃避或压倒Lcn2结合。
Iron is essential for many cellular processes and is required by bacteria for replication. To acquire iron from the host, pathogenic Gram-negative bacteria secrete siderophores, including enterobactin (Ent). However, Ent is bound by the host protein lipocalin 2 (Lcn2), preventing bacterial reuptake of aferric or ferric Ent. Furthermore, the combination of Ent and Lcn2 (Ent + Lcn2) leads to enhanced secretion of interleukin-8 (IL-8) compared to that induced by either stimulus alone. Modified or structurally distinct siderophores, including yersiniabactin (Ybt) and glycosylated Ent (GlyEnt, or salmochelin), deliver iron to bacteria despite the presence of Lcn2. We hypothesized that the robust immune response to Ent and Lcn2 requires iron chelation rather than the Ent + Lcn2 complex itself and also can be stimulated by Lcn2-evasive siderophores. To test this hypothesis, cultured respiratory epithelial cells were stimulated with combinations of purified siderophores and Lcn2 and analyzed by gene expression microarrays, quantitative PCR, and cytokine immunoassays. Ent caused HIF-1 alpha protein stabilization, induced the expression of genes regulated by hypoxia-inducible factor 1 alpha (HIF-1 alpha), and repressed genes involved in cell cycle and DNA replication, whereas Lcn2 induced expression of proinflammatory cytokines. Iron chelation by excess Ent or Ybt significantly increased Lcn2-induced secretion of IL-8, IL-6, and CCL20. Stabilization of HIF-1 alpha was sufficient to enhance Lcn2-induced IL- 6 secretion. These data indicate that respiratory epithelial cells can respond to bacterial siderophores that evade or overwhelm Lcn2 binding by increasing proinflammatory cytokine production.